1. Field of the Invention
The present invention pertains to connectors utilized in printed circuit board packaging, and more particularly, to a method for measuring the real contact area in connectors.
2. Description of the Prior Art
When a pin is intended to mate with a receptacle or a connector in the same manner that an electrical plug mates with its female receptacle, the apparent area of contact of the pin vis-a-vis the receptacle is different than the actual, real area of contact of the pin vis-a-vis the receptacle. The surface of the pin comprises a multitude of peaks and valleys (otherwise termed asperites). In addition, the surface of the receptacle or connector also comprises a multitude of peaks and valleys. When the pin mates with its receptacle or connector, a portion of the surface of the pin mates with a corresponding portion of the surface of its receptacle or connector. The portion of the surface of the pin which mates with the corresponding portion of its receptacle is usually less than the total surface area of the pin. For example, the surface of the peaks associated with one contact area (e.g. the pin) may contact or mate with the surface of the peaks associated with the other contact area (the connector). Therefore, the total surface area of the portion of the surface of the pin which contacts or mates with the corresponding portion of the surface of its receptacle corresponds to the actual, real area of contact whereas the total surface area of the pin corresponds to the apparent area of contact. In the example, the total surface area of the peaks of the one contact area corresponds to the actual, real area of contact whereas the total surface area of the peaks and the valleys corresponds to the apparent area of contact. In connector technology, a determination of the real contact area is important in a subsequent determination of the surface resistance of the pin vis-a-vis its receptacle.
In the field of printed circuit board packaging technology, a chip is mounted on a substrate, and the substrate is connected to a printed circuit board via a pin and a female connector receptacle. As a result of a need for an increase in the performance of computing systems, the number of circuits on the chip and the number of chips has increased. An increase in the number of circuits on the chip necessitates an increase in the number of pins on the substrate to power and provide a signal to the additional circuits on the chip. However, if the pin-to-connector surface resistance is too high, the signal current and the power current energizing the circuits on the chip will encounter an undesirable delay during its attempt to traverse the connector-to-pin interface. This delay results in a decrease in the performance of the circuits on the chips. Therefore, an accurate method for measuring the real contact surface area of the pin surface and the real contact surface area of the connector surface is very important in determining the surface resistance of the pin and the surface resistance of the connector and in further determining the expected performance of the circuits on the chips.
In the prior art, one method of measuring the real contact surface area was to mate two surface areas (e.g.--a pin and a connector) and to inject a corrosive gas into the interface region between the two surface areas. The gas would attack and corrode the valleys but would not corrode the peaks associated with each surface area. The surface area associated with the non-corroded peaks could be measured. However, a corrosive gas does not react with a noble metal, such as Gold.
Another prior art method of measuring the real contact surface area in connectors was to mate the two surface areas of the connector and to expose the two surface areas to a high voltage pulse. The high pulse would melt the areas of the connector which were in contact with one another. The surface area associated with the melted regions could be measured. However, the real contact surface area of a connector contact surface is changed due to the melting of the areas of the connector (the peaks) which are in contact with one another.
Still another prior art method is the so-called "metal on glass" technique. In this method, a connector contact surface is pressed against the surface of glass. The real contact surface area may be visually seen and therefore measured through the glass. However, the real contact surface area is changed when the connector contact surface is pressed against the glass. Furthermore, the measurement of the real contact surface area is dependant upon the specific properties of the glass.
Therefore, each of the above three prior art techniques are subject to error which results in an erroneous determination of the real contact surface area of a connector contact surface.